The light emitting diode (LED) source has several advantages of high efficiency, long life and no harmful substances such as Hg and the likes. With the rapid development of LED technology, the LED's performance, such as brightness, lifetime and the likes, have been greatly improved, such that it has found an increasing application in a variety of areas ranging from outdoor lighting such as street lamps to indoor lighting such as decorative lights, in which LED is used or replaced as a light source.
The LED packaging structure of surface mounted type (SMD) has become a major form of package for its advantages of application convenience and small volume. Refer to FIG. 1, which is a surface mounted LED structure commonly used in prior art, including a packaging bracket 100 and an LED chip 200 mounted in the packaging bracket 100 by die attach process. Metal leads 500 are arranged on the surface of the packaging bracket 100. Electrodes 400 are arranged on the leads 500 on both sides of the LED chip 200. The positive and negative electrodes of the LED chip 200 are electrically connected to the electrodes 400 on the packaging bracket 100 by gold wires 300, respectively. Through phosphor coating and adhesive encapsulating processes, an encapsulation adhesive 600 is filled above the LED chip 200, thereby completing the packaging of the LED chip 200. However, there are the following problems with this present surface mounted LED structure: because the packaging bracket 100 is fanned by using a metal bracket as the substrate and then cutting it after an adhesive is encapsulated by means of plastic injection grooves or molded shape, it results in poor temperature tolerance, non-ideal heat dissipation and difficult miniaturization. Moreover, because the LED chip 200 is face-up mounted and the structure of gold wires 300 for connecting electrodes is used, the connection failure of gold wires is often the failure mode mostly occurred during the production and use of LED. In addition, the face-up mounted LED chip 200 dissipates heat through sapphire, but has poor heat dissipation effect.
To address the problems existing in the above packaging bracket, a better approach is to use a silicon substrate directly as the packaging substrate of the LED chip. At present, the products of SMD structure based on the silicon substrate still cannot enjoy mass sales and applications in practice, and only some related patents are reported. What is mostly used by them is to: dig a deep groove on the upper surface of the silicon wafer, then dig vias in the groove, connect the electrode in the groove on the upper surface to the lower surface, and form a SMD packaging form; embed the LED chip in the silicon groove, and fill the groove with phosphor and an adhesive at the time of packaging; furthermore, commonly use face-up chips of gold wire bonding. The flip-chip structure is partly used with reference to FIG. 2, the packaging structure including a silicon substrate 10, an LED chip 20 and a packaging adhesive 30, wherein the upper surface of the silicon substrate 10 has a deep groove, the LED chip 20 is flip-chip mounted in the deep groove of the silicon substrate 10. Vias 50 are provided in the groove of the silicon substrate 10 corresponding to the positive and negative electrodes of the LED chip 20. The lower surface of the silicon substrate 10 corresponding to the vias 50 has conductive pads 60 and 70, to which the LED chip 20 is electrically connected by the leads provided in the vias 50. The packaging adhesive 30 is formed by filling the deep groove with phosphor and the encapsulant adhesive. There are the following disadvantages of this kind of structure. The silicon wafer is required to experience corrosion for a long time due to the need for digging a large and deep groove on the upper surface the silicon wafer, with the process complex and the cost higher. Simultaneously with the groove very deep, the difficulty in its internal wiring is increased. Especially if the flip chip is used, it is required to make metal bumps on the electrodes of the groove, with the process difficult. Furthermore, because there is the deep groove on the upper surface of the silicon substrate, it is not easy to integrate LED's peripheral functional circuits (such as anti-static protection circuit, driver circuit, etc.) on the silicon substrate, with the application prospects limited. In addition, the number of chips placed in the groove is limited by the size of the groove, thereby not easy to achieve multi-chip modules.
In the process of production and operation of the light-emitting diode, it is easily damaged by electrostatic, resulting in LED failure, so currently most of the LEDs need to be additionally connected to Zener for electrostatic protection in the packaging process, with the additional operation and cost. The LED is actually a PN junction diode and needs DC power drive to operate. Its operating voltage is determined by the material and PN junction characteristics and is essentially constant, so that its brightness is determined by the operating current. Therefore, to ensure the normal operation of the LED, constant current source drive is generally required, to keep the current constant, so that the LED needs an additional power constant current drive system. In addition, LED's peripheral circuits also includes rectifier circuits (i.e. AC-DC conversion circuit), dimming circuit, load monitoring and diagnosis, etc. These functional circuits are individually packaged with large volume and high cost, but these circuits are actually the integrated circuits manufactured by silicon process. If a part of the circuits can be integrated in the silicon substrate, the degree of integration will be effectively improved, with improved stability and reduced costs.